[clang] Add install targets for API headers

[smeenai]

Summary

Add an install target for clang's API headers, which allows them to be
included in distributions. The install rules already existed, but they
lacked a component and a target, making them only accessible via a full
install. These headers are useful for writing clang-based tooling, for
example. They're the clang equivalent to the llvm-headers target and
complement the clang-libraries target.

[smeenai]

I'm not entirely happy with the name clang-dev-headers, and am open to suggestions. It's unfortunate clang-headers was already taken for something different, but renaming that target or increasing its scope seems bad for existing users. Other possibilities I thought of include clang-tooling-headers, though that might be confused with the headers for libTooling specifically, and clang-library-headers. I'm open to suggestions.

[phosek]

In D58317#1400223, @smeenai wrote:

I'm not entirely happy with the name clang-dev-headers, and am open to suggestions. It's unfortunate clang-headers was already taken for something different, but renaming that target or increasing its scope seems bad for existing users. Other possibilities I thought of include clang-tooling-headers, though that might be confused with the headers for libTooling specifically, and clang-library-headers. I'm open to suggestions.

We could consider renaming clang-headers to e.g. clang-resource-headers and then reusing the name which would match llvm-headers. What do you think about that?

[smeenai]

In D58317#1404961, @phosek wrote:

In D58317#1400223, @smeenai wrote:

I'm not entirely happy with the name clang-dev-headers, and am open to suggestions. It's unfortunate clang-headers was already taken for something different, but renaming that target or increasing its scope seems bad for existing users. Other possibilities I thought of include clang-tooling-headers, though that might be confused with the headers for libTooling specifically, and clang-library-headers. I'm open to suggestions.

We could consider renaming clang-headers to e.g. clang-resource-headers and then reusing the name which would match llvm-headers. What do you think about that?

I like that, but I'm worried about breaking existing users of the clang-headers target (e.g. in their build scripts or distributions). I could post on cfe-dev and wait for dissent/consensus, I guess, but if there's an option which doesn't involve breaking backward compatibility, maybe that's preferable.

[phosek]

In D58317#1404966, @smeenai wrote:

In D58317#1404961, @phosek wrote:

In D58317#1400223, @smeenai wrote:

I'm not entirely happy with the name clang-dev-headers, and am open to suggestions. It's unfortunate clang-headers was already taken for something different, but renaming that target or increasing its scope seems bad for existing users. Other possibilities I thought of include clang-tooling-headers, though that might be confused with the headers for libTooling specifically, and clang-library-headers. I'm open to suggestions.

We could consider renaming clang-headers to e.g. clang-resource-headers and then reusing the name which would match llvm-headers. What do you think about that?

I like that, but I'm worried about breaking existing users of the clang-headers target (e.g. in their build scripts or distributions). I could post on cfe-dev and wait for dissent/consensus, I guess, but if there's an option which doesn't involve breaking backward compatibility, maybe that's preferable.

I'd give it a try, if there's a pushback then I'd prefer to go with clang-library-headers.

[smeenai]

Switch to clang-library-headers pending cfe-dev discussion

[smeenai]

Update description

[smeenai]

Update target name

[smeenai]

@phosek This is using the clang-headers name now.

[smeenai]

Ping (although I'm not planning to land this until Monday).

[phosek]

LGTM

clang/CMakeLists.txt

 include_directories(BEFORE
   ${CMAKE_CURRENT_BINARY_DIR}/include
   ${CMAKE_CURRENT_SOURCE_DIR}/include
   )
 
 if (NOT LLVM_INSTALL_TOOLCHAIN_ONLY)
   install(DIRECTORY include/clang include/clang-c
     DESTINATION include
+    COMPONENT clang-headers
     FILES_MATCHING
     PATTERN "*.def"
     PATTERN "*.h"
     PATTERN "config.h" EXCLUDE
     PATTERN ".svn" EXCLUDE
     )
 
   install(DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/include/clang
     DESTINATION include
+    COMPONENT clang-headers
     FILES_MATCHING
     PATTERN "CMakeFiles" EXCLUDE
     PATTERN "*.inc"
     PATTERN "*.h"
     )
 
+  # Installing the headers needs to depend on generating any public
+  # tablegen'd headers.
+  add_custom_target(clang-headers DEPENDS clang-tablegen-targets)
+  set_target_properties(clang-headers PROPERTIES FOLDER "Misc")
+  if(NOT LLVM_ENABLE_IDE)
+    add_llvm_install_targets(install-clang-headers
+                             DEPENDS clang-headers
+                             COMPONENT clang-headers)
+  endif()
+
   install(PROGRAMS utils/bash-autocomplete.sh
     DESTINATION share/clang
     )
 endif()
 
 add_definitions( -D_GNU_SOURCE )
 
 option(CLANG_BUILD_TOOLS

clang/docs/ReleaseNotes.rst

 --------------------
 
 These are major changes to the build system that have happened since the 8.0.0
 release of Clang. Users of the build system should adjust accordingly.
 
 - In 8.0.0 and below, the install-clang-headers target would install clang's
   resource directory headers. This installation is now performed by the
   install-clang-resource-headers target. Users of the old install-clang-headers
-  target should switch to the new install-clang-resource-headers target.
+  target should switch to the new install-clang-resource-headers target. The
+  install-clang-headers target now installs clang's API headers (corresponding
+  to its libraries), which is consistent with the install-llvm-headers target.
 
 -  ...
 
 AST Matchers
 ------------
 
 - ...